Field of the Invention
The present invention relates to control of lifting and lowering of a tray on which sheets are stacked.
Description of the Related Art
Conventionally, there has been known a sheet processing apparatus for performing post-processing, such as punching, stapling, and sorting, on sheets conveyed from an image forming apparatus, such as a copying machine.
Further, in Japanese Patent Laid-Open Publication No. 2007-062921, there has been proposed a sheet processing apparatus that performs post-processing on sheets conveyed from an image forming apparatus and then discharges the sheets such that the sheets are stacked on a stacking tray. The sheet processing apparatus lifts or lowers the stacking tray according to the number of the sheets stacked on the stacking tray.
However, the sheet processing apparatus sometimes suffers from the following problem: The stacking tray projects outward from the apparatus body, and hence an obstacle may be placed e.g. on a floor below the stacking tray. Assuming that there is an obstacle 1400 below a stacking tray 7000, as shown in FIG. 14, when the stacking tray 7000 is lowered, the obstacle 1400 interferes with the stacking tray 7000, which prevents further lowering of the stacking tray 7000.
In this case, it is impossible to discriminate whether the lowering of the stacking tray 700 has been prevented by the interference of the obstacle 1400 or by failure of a motor for driving the stacking tray 7000. For this reason, it is not appropriate to continue a job, and therefore the job has to be temporarily stopped. As a consequence, the job cannot be resumed until a user notices the interruption of the job, performs an appropriate recovery operation, and then instructs the image forming apparatus to resume the job. Thus, downtime continues until the resumption of the job.
In a case where it is not due to motor failure that the stacking tray 7000 cannot be lowered, it is sometimes possible to execute a job if it becomes possible to lower the stacking tray 700 e.g. by removal of products from the stacking tray 700.
Conventionally, however, even when it was not due to motor failure that the stacking tray 700 could not be lowered, and also it becomes possible to resume the job, the image forming apparatus cannot detect this, and a user cannot immediately notice the same either. For this reason, a wastefully long downtime can occur.